1. Field of the Invention
This invention relates to vehicular automatic and semi-automatic mechanical transmission systems and, in particular, to mechanical transmission systems of the type providing at least partially automatic implementation of selected changes or shifting of compound range type transmission gear ratios. More particularly, the present invention relates to a control system for controlling the shifting of mechanical range type compound transmission requiring only speed inputs indicative of input shaft and mainshaft rotational speeds.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior art. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
While such semi-automatic mechanical transmission systems are very well received as they are somewhat less expensive than fully automatic transmission systems, allow manual clutch control for low speed operation and/or do not require automatic selection of the operating gear ratio, they may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained.
Systems for automatic control of compound mechanical transmissions utilizing speed signals from the input shaft and the output shaft are known, as may be seen by reference to U.S. Pat. No. 4,722,248, the disclosure of which is hereby incorporated by reference. Such control systems may be less than satisfactory as the output shaft speed sensor is often in an exposed location, subjecting same to potential tampering and/or damage and/or during a compound shift, with the mainsection in neutral, the input and output shafts are not related in a known manner and thus completion of the auxiliary range shift cannot be confirmed by processing signals indicative of input and output shaft speeds.